How the Ear Works

Anatomy of the Ear

The ear has three main parts: the Outer, the Middle, and the Inner ear.

• The outer ear consists of the visible portion of ear and the ear canal.  The eardrum separates the ear canal from the middle ear.
• The middle ear is an air-filled cavity that houses the small bones of the middle ear.  it is connected to the Eustachian tube, which keeps the pressure within the middle ear the same as the environment.  The small bones (ossicles) in the middle ear help transfer sound to the inner ear.
• The inner ear is a fluid filled, snail shaped structure called the cochlea.  It contains the auditory sensory cells (called hair cells) that are specially tuned to particular tones, similar to a piano.   Attached to the inner ear is the auditory nerve, which takes the signals from the hair cells and sends them to the brain.  The balance system is closely associated with the hearing system.  The balance and hearing nerves are somewhat intertwined and both systems share the same fluids. Dizziness, balance problems, and vertigo can go hand in hand with tinnitus and hearing loss. 

Sound travels as vibrations or sound waves through the air. These waves are caught by the outer ear, funneled down the ear canal and strike the eardrum, causing it to vibrate. The vibrations are passed through the small bones of the middle ear, which transmit them to the inner ear.  The vibrations create a wave in the inner earthat travels up the cochlea and causes the hair cells to be stimulated.  When stimulated, the hair cells transmit the signals along the nerve directly to the brain.  The brain then interprets the signals as sound (music, voice, air conditioner, etc.).

Common Signs Associated with Hearing Loss

• Asking people to repeat what they said 
• Ringing, buzzing, hissing or roaring sounds in the ear
• Misunderstanding conversations
• Complaining that people mumble
• Difficulty hearing and understanding conversations in noisy environments, more so than those around you
• Depending on another to fill you in on the conversation
• Difficulties understanding speakers at public meetings or religious services
• Unwarranted fatigue and stress at the end of the day
• Strained personal and family relationships
• Avoiding social situations

Types of Hearing Loss

• Conductive hearing loss:  A loss of hearing sensitivity due to a dampening of sounds as they travel towards the inner ear.  This can be due to fluid in the middle ear, eardrum injury, or damage to the bones of the middle ear.  
• Sensorineural Hearing loss:  A loss of hearing sensitivity due to damage to the sensory cells that recognize sounds and transmit sounds to the brain via the auditory nerve.
• Mixed Hearing loss:  A combination of both conductive and sensorineural loss.

Degree of Hearing Loss

• Mild hearing loss: speech sounds muffled or indistinct when the speaker is not facing you and is more than a few feet away.  Unable to hear soft sounds, difficulty understanding speech clearly in noisy environment or at a distance.  For children, a mild hearing loss can negatively effect speech and language development and learning.  The scores across the audiogram would average around 25-40 dB HL.
• Moderate hearing loss: unable to hear soft and some moderate sounds; considerable difficulty understanding speech, particularly when in background noise. Can hear speech when in quiet with the speaker raising their voice significantly. In noisy backgrounds, speech understanding is very poor.  45-65 dB pure-tone average.
• Severe hearing loss: some loud sounds are audible but communication in quiet without a hearing instrument is extremely difficult. In noisy backgrounds, speech understanding is impossible.  70-90 dB pure-tone average.
• Profound hearing loss: some very loud sounds are audible but communication without a hearing instrument is not possible.  95 dB or greater pure-tone average.

For a good explanation of the audiogram and types of hearing loss, see  www.earinfo.com/howread1.html